Figure 9-4.-Layout of the staves around the tank bottom, 250-barrel capacity tank.

end toward the small end of the deck section. The flanged side of the deck section acts as a supporting rafter for the deck section. A bolt retainer angle is attached to the inside face of each deck section, flanged to retain the radial seam joint bolts that are installed near the right edge of each deck section.

SPECIAL SECTIONS.-The tank bottom has one special section, fitted with a blind opening. Four of the ten staves are special sections. One section is for a cleanout cover, and the other three sections are used for pipe connections. The tank deck has three special sections. Two sections are used for a combination thief hatch and vent, and one section is used for a liquid level indicator.

EMERGENCY VENT.-An 8-inch vent is bolted to the top cover of the manhole attached to the top of the center ladder supports.

500-BarreI Tank The 500-barrel tank (fig. 9-5) has a capacity of 21,000 gallons of liquid and is similar to the 250- barrel tank, except that the bottom consists of 14 wedge-shaped plates around a one-piece center section, as shown in figure 9-6. This vertical, bolted

Figure 9-5.-500-barrel capacity vertical, bolted steel tank assembled.